In order to achieve a high productivity, a multi-stage film-forming device configured to collectively process a plurality of wafers which are stacked in multiple stages has recently been developed. As for a method of conveying wafers to the multi-stage film-forming device, a method of sequentially conveying the wafers, one by one, to respective stages by a scara-type robot is used. In this method, when the wafers are conveyed to all the stages of the multi-stage film-forming device, the wafers are conveyed by the scara-type robot by the number of times corresponding to the number of the stages of the film-forming device, resulting in an increase of a time required for conveyance of the wafers.
Accordingly, a method of simultaneously holding a plurality of wafers by a plurality of substrate placement racks, and collectively conveying the wafers so as to shorten a time required for conveyance of the wafers has been disclosed (see, e.g., Japanese Patent Laid-Open Publication No. H10-340940).